ALBERT

Description: Proximal evidence of the surface ocean response to the size reduction of the Greenland Ice Sheet (GIS) during the Last Interglacial (MIS5e) and preceding glacial termination (T2) remains largely elusive. Using a new sediment record from the western Iceland Sea, the behavior of the northeastern GIS and its relation to the (subpolar) North Atlantic surface hydrography is examined. Extremely light oxygen isotopic (delta18O) values are found off central East Greenland during early MIS5e and point to enhanced meltwater release, potentially from the northeastern sector of the GIS. Data from downstream the cold East Greenland Current (EGC) and its eastward branches suggest a far-reaching effect of this meltwater not only in the Nordic Seas but also in the SE Labrador Sea. In particular, whereas an early MIS5e warming (at ~128.5-126.5 ka) in the two regions coincided with the relative reduction of meltwater input into the EGC, the subsequent cooling noted at ~126.5 ka followed a renewed major freshwater event off central East Greenland. Our data further indicate persistent freshwater influence from the East Greenland margin over the entire MIS5e interval and, in addition, also reveal a late MIS5e meltwater event. The latter event occurred just prior to the last glacial inception and emphasizes the importance of Greenland meltwater as forcing factor on Interglacial climates.

Description: Paleorecords and modeling studies suggest that instabilities in the Atlantic Meridional Overturning Circulation (AMOC) strongly affect the low-latitude climate, namely via feedbacks on the Atlantic Intertropical Convergence Zone (ITCZ). Despite the pronounced millennial-scale overturning and climatic variability documented in the subpolar North Atlantic during the last interglacial period (MIS 5e), studies on cross-latitudinal teleconnections remain very limited. This precludes a full understanding of the mechanisms controlling subtropical climate evolution across the last warm cycle. Here, we present new planktic foraminiferal assemblage data combined with δ18O values in surface and thermocline-dwelling foraminifera from the Bahamas, a region ideally suited to studying past changes in the subtropical ocean and atmosphere. Our data reveal that the peak sea surface warmth during early MIS 5e was intersected by an abrupt millennial-scale cooling/salinification event, which was possibly associated with a sudden southward displacement of the mean annual ITCZ position. This atmospheric shift is, in turn, ascribed to the transitional climatic regime of early MIS 5e, which was characterized by persistent ocean freshening in the high latitudes and an unstable AMOC mode.

Description: The carbonate content was calculated as CaCO3=8.33x(TC-TOC) using LECO analyzer. Samples were taken at 20 cm throughout the upper ~10.4 m of the core and at 5 cm between 10.4-22 m (revised depth).

Description: The dataset includes stable oxygen (δ¹⁸O) and carbon (δ¹³C) isotope ratios and magnesium to calcium (Mg/Ca) ratios in Globigerinoides ruber (white), reconstructed sea surface temperatures and salinities and planktic foraminifera assemblages of Caribbean sediment core M35003-6. δ¹⁸O, δ¹³C and Mg/Ca data were obtained using 60 specimens of G. ruber (white) sensu stricto picked from the 〉150 µm fraction. δ¹⁸O and δ¹³C values in G. ruber (white) were measured using a Finnigan MAT 253plus mass spectrometer coupled to an automated carbonate preparation ("Kiel") device at Isotope Laboratory at Faculty of Geosciences, University of Bremen. δ¹⁸O and δ¹³C values are expressed relative to the VPDB standard notation (VPDB). The long-term 1σ analytical uncertainty of the standard analyses was better than ±0.07 ‰ for oxygen and ±0.04 ‰ for carbon. Mg/Ca values were measured using a Perkin Elmer Optima 3300 R inductively coupled plasma optical emission spectrophotometer (ICP-OES) at MARUM, University of Bremen. The analysis was performed following the cleaning procedure described in Mohtadi et al. (2014, doi:10.1038/nature13196) and Barker et al. (2003, doi:10.1029/2003GC000559). Mg/Ca values are expressed in mmol/mol. The average 1σ analytical precision is ±0.01 mmol/mol. Replicate samples (n=3) revealed an average 2σ standard deviation of 0.11 mmol/mol. SST, SSS and their uncertainties were calculated in PSU-Solver (Thirumalai et al., 2016; doi:10.1002/2016PA002970) from coupled δ¹⁸O-Mg/Ca values in G. ruber (white) using equations of Kısakürek et al. (2008, doi:10.1016/j.epsl.2008.06.026; Bemis et al., 1998, doi:10.1029/98PA00070; LeGrande and Schmidt, 2006, doi:10.1029/2006GL026011). The average 1σ (2σ) uncertainties are about ±0.5 (0.8) °C for SST and ±0.3 (0.6) units for SSS. These errors include calibration errors, 2σ combined analytical and sampling uncertainty for Mg/Ca (±0.11 mmol/mol) and 2σ analytical uncertainty for δ¹⁸O (±0.14 ‰). Planktic foraminifera species and lithic grains were counted in the size fraction 〉150 µm; minimum of 600 specimens has been identified per sample. Large specimens of N. dutertrei were counted together with smaller juvenile specimens referred to as N. dutertrei-N. pachyderma (dextral)-intergrades.

Description: Stable isotope ratios in planktic foraminifera were measured every 20 cm for the upper 0-18.5 m and every 10 cm between 18.5-22 cm (revised depth). Note that the original core depth scale in core MD99-2198 was modified by excluding two intervals (10.06-10.24 m and 13.78-14.30 m), representing episodes where the core was ripped apart, as could be concluded on the basis of large increases in porosity.